Dehydration process and catalyst



Patented May 25, 1948 DEIIYDIATION PROCESS AND CATALYST William 3. Hale,Midland, Mich, assignor to National Agrol Company, Inc., Washington,D.0. ,aeorporation of Delaware No Drawing. Application December 16,1942,

Serial No. 469,256

1 claim. (Cl. zen-cs1) but generally sulphuric acid and organic sul- Vphonic acids in small quantities have been previously employed for thispurpose. These prior processes have not been especially emcient becauseof the low yield and the production of undesirable by-products. Forexample, in the dehydration of pinacol by these methods, a substantialpercentage of pinacolin is produced. Moreover, the time required forthese processes is appreciably longer than that required by the presentprocess.

One of the objects of this invention is to avoid the above mentioneddisadvantages of the prior art.

Another object of the present invention is to provide a method of.dehydrating dihydric aliphatic glycols, such as pinacol, by bringing itinto contact with an especially prepared catalyst under controlledconditions.

A further object of this invention is to provide an especially preparedcatalyst which is preferably used in this process of dehydration.

With these and other objects in view, which will be apparent from thesubsequent description, this invention embraces broadly a process ofdehydrating dihydric aliphatic glycols by contactingthe selected glycolwith an especially prepared catalyst; and also a catalyst which ispreferably employed in this process and a method of, making the same.The dehydratidn process 2 v form of this catalyst disclosed in thepresent application comprises a skeletal core of a base ,metal selectedfrom the group consisting of beryllium, magnesium, zinc, cadmium,aluminum,

thallium, tin,'lead, bismuth, or related metals,

which extends into the interstices of the nonsintered individualparticles of an acidic oxide of a metal selected from Family A of eitherthe fifth or sixth groups of the periodic system of the elements,notably vanadium, columbium, tantalum, chromium, molybdenum, tungsten,uranium.

In preparing the catalyst, the base metal which is to form the core andthe selected acidic oxide are roasted at a temperature which is justsufficient to bring the base metal to a molten state, and thus permitits penetration into the interstices of the oxide particles to form acatalytic mass of non-sintered pellets which pour freely and do not losetheir original shape. The selected base metal must have a lower meltingpoint than the selected oxide to prevent sintering.

During the formation of this catalyst. the particles of the selectedacidic oxide are partially reduced and at the same time the base metalforming the skeletal core is partially oxidized.

'As a result. a compound is formed by thereaction between the oxidizedportion of this base metal and the acidic oxide, which compound in turnundergoes a certain degree of reduction by contact with the molten freebase metal. A

- substantial portion of the metal of the skeletal is conducted at araised temperature in the presence of water vapor and a nonreactive gas.Large yields of the desired product are obtained as a result of a singlepass of the selected glycol over the catalyst and only an unappreciablepercentage of by-products is produced. For example, the treatmentofpinacol by this method has resulted in conversions to 2,3 dimethylbutadiene as high as 93% without the production of by-products.

The catalyst employed is in the form of pellets core remains freehowever, and serves as a reduction reserve for the partially reducedacidic oxide.

Another catalyst which may be employed is disclosed in my copendingapplication, Serial No. 436,028, filed March 24, 1 42. This catalyst issimilar to the one described above except that the skeletal core iscomposed of any alloy of two or more of the base metals which werepreviously mentioned. It has been found that the use of which pourfreely and do not lose their original shape. The catalyst is stableunder increased conditions of temperature and reduction, and can be usedfor prolonged periods without re-' activation.

One, form of the catalyst which may be em ployed is disclosed in thecopending application by Harry Miller, Serial No. 303,168, filedNovember 6, 1939, now Patent 2,379,736. The

such an alloy enables rapid reduction of theselected acidic oxide atlower temperatures without danger of the skeletal core itself becomingcompletely oxidized. The use of these alloys, furthermore; insures asufilcient reductive reserve.

A third form of the catalyst is disclosed in c0- pending application,Serial No. 451,320, which was filed July 1'7, 1942, by William J. Haleand Harry'Miller', now abandoned. This catalyst may-be similar in formto either of the catalysts previously discussed, but contains anadditional improved ingredient which materially aids in preventing thecomplete reduction of the acidic oxide dur- 3 I the preparation of thecatalyst. 'lhese agents are refractory oxides which react with thepreviously mentioned acidic oxides of Family Act the fifth and sixthgroups of the periodic system to form polyacid anions which retainoxygen even when subjected to extremely rigorous conditions during thepreviously mentioned roasting and reduction steps. Among theserefractory agents maybe mentioned the oxides of boron, cerium and therare earth metals. silicon, titanium, zirconium, thorium, andphosphorous. The me of these refractories eliminates the necessity ofcarefully controlling the temperature during the preparation of thecatalyst to prevent complete reduction. Although the pres-" ence ofthese refractory oxides lengthens the life of the catalyst, occasionsmay arise in which their use is not primarily essential.

The preferred form of the catalyst is an im-,

face are then brought into contact with the se lected acidic oxide andthe selected refractory oxide. if one is employed, and the mass isroasted to form the catalyst in pellet form. These pellets pour freelyand retain their original shape.

One of the methods of preparing the preferred catalyst is given in thefollowing example:

Example 1 A -mesh granular carborundum is heated in a molten bathconsisting of three parts aluminum and one part magnesium for two hoursand then removed, cooled and weighed to determine the metallic content.A quantity of these pellets carrying 100 grams of the alloy is thenbrought into contact with one gram of refractory acidic oxide such asfreshly precipitated silicic acid and 10 grams of powdered tungsticanhydride and the whole thoroughly triturated. The resulting granularmass is then roasted in the air at approximately 500" C. and finallyreduced in an atmosphere of hydrogen at approximately 300 C. until theblue color of the reduced tungstic oxide is fully developed. Thiscatalyst will occupy about cubic inches.

Example 2 4 the form' of vapor is desirable to replace the tendencytowards intro-dehydration of adjacent roups. Usually it is desirable todilute the vapors of glycol with from 15 to of water vapor by volume forthis purpose.

This mixture is further diluted with from 1 to 5 times its volume of anonreactive gas such as carbon dioxide, 'carbonmonoxide, methane,hydrogen, ammonia, the amides or'imldes lust before passage of thevapors over the selected dehydrative catalyst. Reactive gases such asfree oxygen or nitrogen should not be permitted within the reaction zoneas their presence does not favor the formation of the desiredunsaturated carbon compounds. of nitrogen has been found to beundesirable because ofnitride' formation.

The temperature of the reaction should be maintained at as low a pointas possible. Generally a range between 200 and 250 C. has been found tobe preferable, the optimum temperature within this range depending uponthe glycol which is selected.

It will be found that this improved process brings about dehydrationwith the greatest ease, and a high percentage of conversion in-theinitial step. This high percentage of conversion, with practicallycomplete absence of by-products and One, hundred parts of 10 meshgranular 2 aluminum is well triturated with one part freshlyprecipitated silicic acid, two parts tantalum pentoxide, and eight partstungstic anhydride, after which the granular mass is brought to atemperature of approximately 600 C. for a. few moments only, and thencooled and reduced in an atmosphere of hydrogen at approximately 300(7., when it is ready to use.

use of relatively low temperatures is brought out in the followingexamples:

Example 3 Into an ordinary combustion tube of about inch internaldiameter 50 grams of the catalyst, prepared as described in Example 1,was introducedand found to fill over ten inches of tube length. Thetemperature of catalytic mass was now maintained at approximately 200 0.The vapors of 10 grams of pinacol admixed with about 2 grams of watervapor together with about 5 cc.

of an inert gas, such as carbon dioxide, were now passed through thetube within the span of 20 minutes. There resulted 6.3 grams of2,3-dimethyl butadiene (B. P.- 71) corresponding to a93% conversion inone pass, with only 1 gram of pinacol left unacted upon.

Example 4 In an apparatus setup as in Example 3 and with an equal amountof same catalyst contained within the combustion tube, there was nowpassed over the catalyst, maintained at about 220 0., 10 grams of thevapor of 2 methyl butane did-(2.3), (or trimethyl ethylene glycol)((CH1)2.C(OH).CHOH.CH1 B. P. 177 C.) together with 2 grams of watervapor and about 10 cc. of an inert gas such as carbon dioxide in thespan of"'20 minutes. There resulted 7.1 grams of 2-methyl butadiene orisoprene (B. P. 32-33) corresponding to a 92% conversion in one pass. Inthe residual portion of distillate little or no unacted upon trimethylethylene glycol could be detected but in its stead about 1 gram ofpropenyl methyl carbine], was detected.

Example 5 Example 4 was repeated in all details save that for thetrimethyl ethylene glycol was now substituted 10 grams of 2-methylbutane did-(2.4)

or as-dimethyl trimethylene glycol ((CH's):C(OH).CH:.CH:OH) (B. P. 202-3C.). There resulted about 7.3 grams of isoprene corresponding to about94% conversion in one pass.

For example, the presence.

the halfway dehydratedproduct, isoture of furnace at 220 duced 10 gramsof 2-methyl pentane dial-(2.4)

Example 6 Again Example 4 was repeated in all detail save that here wasintroduced grams of pentane did-(2.4) or aa'-dimethyl trimethyleneglycol (B. P. 197-8 C.) (CH3.CHOH.CH2.CHOH.CH3). There resulted 6.1grams of pentadiene -(1.3) or l-methyl butadiene (piperylene) B. P.42-44 C. corresponding to 93% conversion in one pass.

Example 7 Example 4 was now repeated using a closely similar compound tothat recorded in Example 5. Here were introduced 10 grams of pentanediol- (1.4) or y-pentylene glycol (CH3.CHOH.CH2.CH2.CH2OH) B. P. (713mm.) 219-220" C. Practically the same conversion to piperylene wasrecorded here as in Example 6.

. Example 8 Example 4 was again repeated in all detail save that herewas introduced 10 grams of hexane diol-(2.5) or a,a-dimethy1tetramethylene glycol (CH3.CHOH.CH2.CH2.CHOH.CH3) B. P. 2l2-215 C. Thereresulted 6.1 grams of hexadiene-(2.4)

or dipropenyl B. P. 87 C. corresponding to an 88% conversion in onepass.

Example 9 Example 8 was repeated substituting 10 grams of a closelyrelated compound hexane dial-(3.4) or a,a' diethyl ethylene glycol(CH3.CHQ.CHOH.CHCH.CH2.CH3)

B. P. 233-4 C. and raising the temperature of furnace to 250 C. Theyield of dipropenyl was practically identical with that in Example 8.

Example 10 Here again a closely related compound to those in Examples 8and 9 was employed, namely 10 grams of hexane diol-(2.4) or amethyl-a'-ethyl trimethylene glycol (CH:.CHaCHOHCI-IaCHOKCHa) Example 4was again repeated but at tempera- C. There was now introor,a,a'-trimethyl trimethylene glycol ((0113) 2.0(011) .CH2.CHOH.CH3) n.P. (740 mm.) 190-194 c. There resulted 6.3

' 6 grams of 1,3-dimethyl butadiene (1.3) or 2- methyl pentadiene-(L3)B. P. '76-'77 C. corresponding to 91% conversion in one pass.

Example 12 col (CH3.CH2.CHOH.CH2.CH2.CH2OH) B. P. (18.5

mm.) 134-5 C. There resulted 6.4 grams of 1- ethyl butadiene orhexadiene-(l.3)

CH3.CH2.CH:CH.CH1CH2) B. P. 72-4'C. corresponding to 92% conversion inone pass.

Throughout the experiments reported above, substitution of onenonreactive gas for another was found to be perfectly feasible. Indeedthe amines and imines reported in the William J. Hale and Harry Millerapplication, Serial No. 457,478, filed September 5, 1942 now Patent2,400,- 409, were often found beneficial although not especially neededin the examples cited above.

While for purposes of illustration specific examples of this process andpreferred catalyst have been given, it is not intended that theinvention be limited to these examples, as it is believed obvious thatchanges can be made by one skilled in the art without exceeding thespirit of the invention or the scope of the claim.

I claim:

A process for dehydratingpinacol comprising contacting vapors ofpinacol, diluted with 15-25% by volume of water vapor and 1-5 times itsvolume of a nonreactive gas, with an especially prepared catalystcomprising a skeletal core of aluminum which is coated on particles ofgranular carborundum of approximately 10 mesh, and extends within theinterstices of polyacid anions formed by the reaction at raisedtemperatures of silicic acid and tungstic anhydride, said catalyst beingin the form of pellets which retain their original shape and pourfreely.

WILLIAM J. HALE.

' REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

